1. Field
The invention relates to a voltage level control circuit and, in particular, to an operator interface control circuit for digitally providing variable shuttle speed control of a tape transport.
2. Prior Art
Variable shuttle speed control as employed in audio, video, etc., tape transports during, for example, a tape editing process, requires tape speeds ranging from full shuttle speed in either direction during tape transfer, to zero speed when the desired edit location is found. Such variable speed shuttle processes heretofore have been controlled by a standard rotary or linear potentiometer, and include a zero or neutral setting during which no output is generated. The potentiometer is mechanically rotated or linearly slid to either side of the neutral position to generate forward or backward tape transfer at variable shuttle speeds. Accordingly, searching for an edit location in an audio system generally involves transferring tape by selected cranking of the mechanical potentiometer while listening to the garbled audio ("monkey chatter") generated by the high shuttle speed reproduction until a silent spot, etc., is located indicating the desired edit location. The tape is then shuttled back and forth at relatively slower shuttle speeds by jockeying the potentiometer through smaller rotations back and forth across the neutral position until the exact edit location is determined. The potentiometer is then turned to the neutral position to stop the tape. Such a process is cumbersome and time consuming.
In addition, such prior art rotary or linear potentiometers require mechanical or manual reset to the neutral position if and when the transport enters a mode other than the shuttle mode, viz, the stop, record or reproduce modes. Thus if the potentiometer is set to a selected shuttle speed, and the transport is thereafter operated in a different mode, the transport will return to the operating speed previously set upon re-entering the shuttle mode. This is an undesirable condition.